Portable cellular radiotelephones, a typical block diagram of which is illustrated in FIG. 3, have become a popular and convenient means of communication while away from a landline telephone. A radiotelephone user can communicate to other parties around the world while remaining mobile. A limitation of portable radiotelephones, however, is the reduced power and antenna gain compared to mobile radiotelephones.
To overcome these limitations, power boosters or antenna extenders have been mounted in automobiles to connect to the portable. A power booster increases a portable's typical 600 mW power to the power level of a mobile, 3 W. An antenna extender simply couples a portable's antenna to a higher gain antenna mounted on the exterior of the vehicle, thus providing better communications for the portable. The communication system formed by the connection of the portable to the booster or antenna extender uses the memory and functions of the portable while the transmit power from the portable is amplified to the cellular system limit.
The drawback with the power booster/antenna extender in combination with the portable is that the portable must be connected to the system in order to operate. The portability that makes the portable radiotelephone an asset reduces the likelihood that the radiotelephone user will remember to connect the portable to the booster/extender. The user may take the phone into the home or office and forget to connect it to the mobile system until having driven a considerable distance. There is a resulting need to alert the driver that the portable is not present in the booster/extender system.